The invention concerns an optoelectronic component that emits incoherent radiation. In particular, the invention pertains to semiconductor light emitting diodes.
A variety of principles are known for the construction of semiconductor light emitting diodes (LEDs and IREDs), for example, from W. Bludau, Halbleiter-Optoelektronik [Semiconductor Optoelectronics], Munich, Vienna, Hanser-Verlag 1995, pages 92 to 114. The LEDs described therein are, for example, fabricated on the basis of GaP, GaAsP, GaAs, GaAlAs, InGaAsP and InGaN semiconductor material.
A central problem associated with prior art light emitting diodes is the efficient radiation output from the semiconductor body producing the radiation. This takes place either through the front face or through the side faces of the semiconductor body. Some light emitting diodes contain special additional layers for distributing the radiation in order to suppress the total reflection at the outer surfaces of the semiconductor body. As before, however, the external quantum yield of these components is comparatively low.
It is accordingly an object of the invention to provide an incoherent radiation emitting optoelectronic component, which overcomes the above-mentioned disadvantages of the heretoforeknown devices and methods of this general type and which has a higher external quantum yield compared with prior art light emitting diodes.
With the foregoing and other objects in view there is provided, in accordance with the invention, an incoherent radiation-emitting optoelectronic component, comprising:
a radiation generating body formed with a planar optical waveguide having a wave guiding layer arranged between two reflecting layers, the planar optical waveguide defining a direction of wave propagation;
a radiation generating zone formed in the wave guiding layer for generating electromagnetic radiation;
a device formed in the radiation generating body for lateral current pinching in the radiation generating body; and
the wave guiding layer having an outer side face enclosing a given angle with the direction of wave propagation in the planar optical waveguide.
In accordance with an added feature of the invention, the radiation generating body is a semiconductor body.
In other words, in accordance with the invention, a radiation generating body is provided with a planar optical waveguide with a wave guiding layer, and the wave guiding layer has a radiation generating zone. The zone generates an electromagnetic radiation while the component is operating. The planar optical waveguide has at least one lateral output taper over which the radiation generated in the radiation generating zone while the component is operating is output as space radiation from the wave guide into the surroundings of the radiation generating body.
The term xe2x80x9coutput taperxe2x80x9d means quite generally a slanting outer side face of the wave guiding layer of the waveguide, i.e. a side face which is positioned neither parallel nor perpendicular to a direction of wave propagation in the planar optical waveguide. Preferably, the entire side face of the planar optical waveguide is formed as an output taper. These outer areas of the wave guiding layer therefore function as a taper for the photons propagated in the wave guiding layer.
The structure, according to the invention, of the radiation generating body forces the photons emitted by the radiation generating zone into the wave guiding regionxe2x80x94the wave guiding layerxe2x80x94of the planar optical waveguide. The radiation generating zone and the planar optical waveguide are preferably constructed such as to support principally the emission of TE waves and emission in the lateral direction of the planar optical waveguide.
As a result, the electromagnetic radiation generated advantageously strikes the lateral output taper at a defined angle.
In accordance with an additional feature of the invention, the outer side face of the wave guiding layer and side faces of the two reflector layers jointly form a side face oriented at an angle relative to the wave propagating layer.
In accordance with another feature of the invention, each of the two reflecting layers is a Bragg reflector.
In these further preferred embodiments of the radiation emitting optoelectronic component according to the invention, the wave guiding layer is arranged between two highly reflective plane-parallel optical reflecting layers which in the case of a radiation emitting semiconductor body are preferably formed as Bragg reflectors. Such structures are known, e.g. from laser diodes with vertical resonators, where epitaxial Bragg mirrors are mainly used as resonating mirrors (cf. W. Bludau, supra, pages 188-89).
A considerable advantage of this embodiment consists therein that the radiation generating zone, e.g. a radiation generating p-n junction, is positioned between two highly reflective plane-parallel mirrors, which form a low loss planar optical waveguide. This leads to an advantageous significant reduction of optical losses within the waveguide. As an example, epitaxial Bragg mirrors enable reflection factors of over 99% to be realized routinely. Appropriate selection of the thickness of the waveguide also allow the absorption losses within the waveguide to be considerably reduced.
In accordance with again an added feature of the invention, the radiation generating body is a semiconductor body and the radiation generating zone has a single or multiple quantum well structure. Quantum well structures of this kind are, in fact, known in the field of optical semiconductor technology (cf. W. Bludau, supra, pages 18-87).
In accordance with again an additional feature of the invention, the single or multiple quantum well structure is fabricated from compressively strained quantum wells. Such compressively strained quantum wells optimally couple with the TE modes of the planar waveguide formed by the two reflecting layers, preferably Bragg reflectors. The quantum wells are preferably arranged near the node of a standing-wave field formed vertically to the direction of wave propagation of the planar optical waveguide while the component is operating. As a result electromagnetic radiation generated in the radiation generating zone is favored advantageously in the lateral direction, i.e. parallel to the waveguide.
In accordance with again a further feature of the invention, therefore, the optical waveguide is a vertical lateral output taper. Alternatively, the optical waveguide is a horizontal lateral output taper.
In a further preferred embodiment of the component according to the invention the radiation generating body has an essentially cylindrically symmetrical shape whereby the axis of symmetry runs essentially perpendicular to the planar optical waveguide. The radiation generating zone is preferably arranged in such a way that the photons are generated near the axis of the cylindrically symmetrical structure.
As a result of the output taper the radiation modes running outwards in the waveguide are converted into space waves almost without losses and thus effect an optimal light output from the radiation generating body.
In a further especially preferred embodiment the output taper preferably includes an angle of approximately 1xc2x0 to 30xc2x0 with the direction of propagation of the radiation in the planar optical waveguide. In order to further improve the output of the electromagnetic radiation through the output taper this is advantageously provided with an anti-reflection layer.
In addition, in a further advantageous embodiment the entire side face of the planar optical waveguide is formed as an output taper.
Radiation generating bodies according to the invention can advantageously be incorporated in LED cases of prior art, e.g. radial LED cases, SMD cases for laterally or upwardly emitting LEDs or SOT cases, in which they are cast en bloc in synthetic material. However, any other kind of LED case is also conceivable.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an incoherent Radiation Emitting Optoelectronic Component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.